Carbon nanotube field-effect transistors (CNFETs) are promising candidates to substitute silicon transistors. Boasting extraordinary electronic properties, CNFETs exhibit characteristics rivaling those of state-of-the-art Si-based metal-oxide-semiconductor field-effect transistors (MOSFETs). However, as any technology that is in development, CNFET fabrication process still have some imperfections that results in carbon nanotube variations, which can have a severe impact on the devices' performance and jeopardize their reliability (in this work the term reliability means time-zero failure due to manufacturing variations). This paper presents a study of the effects on transistors of the main CNFET manufacturing imperfections, including the presence of metallic carbon nanotubes (m-CNTs), imperfect m-CNT removal processes, chirality drift, CNT doping variations in the source/drain extension regions, and density fluctuations due to non-uniform inter-CNT spacing.